Wiring and electrics nightmare.
 

My 1990 is doing something terrifically wrong, it started sunday and now I've been under the car, through the dash tracing lines through wiring diagrams and I still can't figure it out.

The 80a fuse blew on the car and since I have been unable to figure out why. It only happens when the ignition is in the "start" position, and at the moment I have yet to blow the second 80a I've hooked up, though it does start glowing nearly immediately.

So far I have disconnected the starter, and the alternator. After which the fuse still glows, and I disconnected all other fuses coming off the power before and after the fuse. I've tested the ignition switch and spent plenty of time under the dash looking at wires. None of the ignition switch wires seem grounded out according to the multimeter.

I need help! I'm sure there are things I've tested I'm forgetting to mention, but any recommendations will be taken seriously.

80A is a lot of current. I would imagine if it was a normal wire someplace you could just follow the smoke. Or at least feel for warm wires leaving the fuse box.

If you pull the connector off of the ignition and short the white to the black/blue does the 80a still glow? If not the problem is the ignition switch.

If it still glows, try the same connector remove/short on the clutch switch.

You could pull all the other fuses, hold the ign in start and put fuses back in until you find the one that starts to make it glow.

I'm going to look into shorting white to black/blue today I'm hoping the 80a won't still glow, though replacing the ignition switch would be a pita. Maybe just replace it with toggles and a push button! >_>

All the other fuses had been removed from the fuse box and the 80a still glowed.

sounds like a nightmare...

You already know this but JIC, there are two fuse boxes. Under the dash, driver's foot and under hood, passenger fender.

I kind a trying to visualize your terrible nightmare. Is there a way to re-route another wire and completely forget about that one by simply cutting and securing it?

You know like to hell with that power source and run another one nearby.

Yes, I know there are 2 fuse boxes. I did not remove the interior fuses to see if they would effect the 80a glow, and at the moment I don't have a wiring diagram in front of me, but I'm guessing I didn't because it would make much sense to.

I do know though, thinking about it that the blue line going off the ignition switch goes through the top line of fuses in the interior (I believe?)

So the main fuse glows / pops, only when the key is in the "start" position, but not the "run" position. Correct?

You say you disconnected the starter- was this only the large white wire on the ring terminal, or did you also pull the thinner black/red wire? That's the one that's pulling current through the 80A Main fuse when in "start" (and also with the clutch depressed, assuming you haven't bypassed that switch.)

Which begs the question- does this happen when you do*not* depress the clutch (again, assuming that you normally have to in order to engage the starter)?

Yes only in "start" does it glow but not in the On position. In fact, everything seems fine in the on position, I can roll up or down the windows, get lights in the interior.

Yes I disconnected everything from the starter. I actually took it down to autozone to get it tested.

I did actually remove the switch as a problem, though I just ziptied it closed so I don't have to push the clutch down. At some point during multimeter play I had taken the zipties off the switch (likewise unplugging it does the same), though I never tried turning the key over with the fuse in and battery etc, like that. Certainly can try that it's easy enough.

I'd definitely check it without the switch depressed. Reason is that there are only a very few things in the car that get powered by the keyswitch "Start" position, and having that switch open will sort of divide the problem in half.

Basically, you've got power coming in from the battery through the 80A fuse, which goes to the keyswitch on the white wire. Then, coming out of the keyswitch is the black/blue wire which goes straight to the clutch switch. After the clutch switch it's a black/red wire which goes to the starter itself, the "ST SIGN" fuse, and the blower motor relay. (This last one is a tad counter-intuitive, the starting circuit hot wire actually provides the ground for the blower relay, taking advantage of the low impedance across the starter solenoid to allow the relay to close when the solenoid is unpowered, but prevent the relay from closing when there is voltage being applied to the solenoid. Trust me, it makes sense if you're a EE, and seems utterly idiotic if you're not.)


So, short list: try it with the clutch switch not engaged. If it still cooks the fuse, you're got a short circuit upstream from there. Remove the blower relay before probing further with your ohmmeter, as it'll throw off your tests. It's highly unlikely that the fuel pump relay part of the circuit is at fault, as the 10A ST SIGN fuse would have popped. (Could be a short upstream of it, I guess.)

http://img40.imagefra.me/img/img40/7...1m_b23fec2.gif

http://img37.imagefra.me/img/img37/7...2m_9780908.gif

http://img37.imagefra.me/img/img37/7...3m_e444839.gif

Almost forgot, that circuit also hits the instrument cluster.

http://img37.imagefra.me/img/img37/7...4m_8711098.gif

Thanks for everything Joe.

I did some more testing, took appart the gauge cluster, and really did not see anything suspicious. I was really getting frustrated and last on my list was testing the ignition switch, especially since I had been there testing it with a multimeter already. So from there I started testing the wires going to the ignition switch, jumping certain cables together. Doing this directly I did not find the fuse to glow, and I could hear a relay or solinoid clicking over (starter was not installed at the time). With those good signs I started attaching more and more fuses and accessories and still the fuse did not glow. Finally threw everything together and it ran. :shrug: I have a feeling this nightmare will pop up some time later down the road.

Sounds like a nightmare of a short. Hopefully it stays gone!!!